Satoru Iwata, the affable and hands-on president of Nintendo Co., died on Saturday after a lengthy battle with illness. He was 55.

Mr. Iwata was one of the most revered and popular gaming executives in the world, and is credited with guiding the Kyoto, Japan-based gaming giant through some of its most prosperous and most challenging periods.

President of the company since 2002 – and the first president from outside Nintendo’s founding Yamauchi family – Iwata came from a software engineering and game design background. Prior to taking the helm of Nintendo, he helped the company develop some of its most popular games, including "Super Smash Bros." for the Nintendo 64 with star characters like Mario and Donkey Kong. The game was the first in a series of lucrative fighting games that sold in the tens of millions.

Even after Iwata joined Nintendo from the company’s Tokyo-based affiliate HAL Laboratory in 2000 he continued to work personally on Nintendo’s products, including several titles in the company’s popular Pokémon series.

“He didn’t just create technology. He created a whole culture,” said Nobuyuki Hayashi, a consultant and technology expert, in an interview with the Associated Press.

“It wasn’t just a consumer product that he had delivered. He brought to people something that’s eternal, what people remember from when they were kids. He was special,” added Mr. Hayashi.

Fans created digital monuments and remembrances to Iwata across the Internet over the weekend. On some sites there was an image of the flag in Super Mario flying at half-staff. Fans on Twitter thanked him for childhood memories and for bringing families together. Bungie, the company behind the Halo and Destiny games, posted an Iwata quote on Twitter: “On my business card, I am a corporate president. In my mind, I am a game developer. But in my heart, I am a gamer.”

"On my business card, I am a corporate president. In my mind, I am a game developer. But in my heart, I am a gamer." - Iwata-san

Iwata was appointed president of Nintendo in 2002, after just two years at the company. His appointment received the personal blessing of Hiroshi Yamauchi, who had led the company since 1949. He was in his early 40s when he became president, a surprisingly young age for a Japanese company.

Nintendo was founded as a playing card company in 1889, but under Mr. Yamauchi and later Iwata it came to be an industry leader in video games. On Iwata's watch, Nintendo released the Nintendo DS, a dual-screen handheld gaming console that succeeded the iconic Game Boy. The DS went on to challenge Sony – maker of the PlayStation consoles – for the title of “bestselling game platform of all time.” The company also released the Wii in 2006, now perhaps the most recognizable game system in the company’s history.

For many in the industry, Iwata will be remembered most for helping the company transition onto mobile devices and smartphones. Nintendo had repeatedly rejected the idea of developing games for mobile devices – including Iwata himself – but in March, after watching rivals Sony and Microsoft Corp. take the lead in mobile gaming, the company announced a partnership with DeNA Co. The alliance with the Japanese mobile gaming company was designed to bring the company’s beloved characters, including Super Mario, to smart phones for the first time.

Products aside, Iwata was beloved for his candid and mischievous personality – an openness rarely seen from gaming executives in any country. He frequently interacted with fans online and emceed the company’s biggest releases. Mark MacDonald, executive director of 8-4, a Tokyo-based game consulting company, told the AP that fan interactions with Iwata were like having “a David Letterman in your living room.”

He was an annual hit at the Electronic Entertainment Expo (also known as E3), where he would announce the arrival of the company’s big new products. At the 2014 conference he appeared in an effects-laden mock kung-fu brawl with Nintendo America president Reggie Fils-Aimé. At the 2015 conference in mid-June he appeared by video link as a Muppet designed by The Jim Henson Company.

This appearance by video, and not in person, was one of the first signs of his failing health. His health problems were first aired after he backed out of the E3 conference last year, according to Time. He became visibly thinner in the ensuing months, Time reported.

Matt Peckham, writing for the magazine, said Iwata would be remembered as much for his personality as his genius as a game developer.

“Iwata had a knack for making interviewers feel at ease,” writes Mr. Peckham. “He’ll be rightly remembered for his triumphs ... but it was his warmth and affability when engaging with strangers that I’ll remember most.”

A replacement has not yet been announced. The company said Shigeru Miyamaoto, designer of Nintendo's first blockbuster games "Donkey Kong," "Zelda," and "Super Mario Bros.," will stay in the leadership team along with game designer Genyo Takeda.

“We will upkeep the development approach that we built with Iwata, and we in the development team hope to keep working as one to build toward the future,” said Mr. Miyamoto in a statement.